Composition for tungsten CMP

ABSTRACT

A chemical mechanical polishing composition for polishing a substrate having a tungsten layer includes a water based liquid carrier, a colloidal silica abrasive dispersed in the liquid carrier and having a permanent positive charge of at least 6 mV, an amine containing polymer in solution in the liquid carrier, and an iron containing accelerator. A method for chemical mechanical polishing a substrate including a tungsten layer includes contacting the substrate with the above described polishing composition, moving the polishing composition relative to the substrate, and abrading the substrate to remove a portion of the tungsten from the substrate and thereby polish the substrate.

BACKGROUND OF THE INVENTION

Chemical mechanical polishing (CMP) compositions and methods forpolishing (or planarizing) the surface of a substrate are well known inthe art. Polishing compositions (also known as polishing slurries, CMPslurries, and CMP compositions) for polishing metal layers (such astungsten) on a semiconductor substrate may include abrasive particlessuspended in an aqueous solution and chemical accelerators such asoxidizers, chelating agents, catalysts, and the like.

In a conventional CMP operation, the substrate (wafer) to be polished ismounted on a carrier (polishing head) which is in turn mounted on acarrier assembly and positioned in contact with a polishing pad in a CMPapparatus (polishing tool). The carrier assembly provides a controllablepressure to the substrate, pressing the substrate against the polishingpad. The substrate and pad are moved relative to one another by anexternal driving force. The relative motion of the substrate and padabrades and removes a portion of the material from the surface of thesubstrate, thereby polishing the substrate. The polishing of thesubstrate by the relative movement of the pad and the substrate may befurther aided by the chemical activity of the polishing composition(e.g., by an oxidizing agent and other chemical compounds present in theCMP composition) and/or the mechanical activity of an abrasive suspendedin the polishing composition.

In typical tungsten plug and interconnect processes, tungsten isdeposited over a dielectric and within openings formed therein. Theexcess tungsten over the dielectric layer is then removed during a CMPoperation to form tungsten plugs and interconnects within thedielectric. As semiconductor device feature sizes continue to shrink,meeting local and global planarity requirements has become moredifficult in CMP operations (e.g., in tungsten CMP operations). Arrayerosion (also referred to as oxide erosion), plug and line recessing,and tungsten etching defects are known to compromise planarity andoverall device integrity. For example, excessive array erosion may leadto difficulties in subsequent lithography steps as well as causeelectrical contact problems that can degrade electrical performance.Tungsten etching/corrosion and plug and line recessing may also degradeelectrical performance or even cause device failure.

Commercially available tungsten CMP slurries commonly make use of ahydrogen peroxide oxidizer. While there are many advantages to the useof hydrogen peroxide, it is known to cause excessive tungsten etching incertain CMP operations. In such operations it may be advantageous toreduce the rate at which tungsten etches (corrodes) in the CMPcomposition. Thus, there is a need in the industry for tungsten CMPslurries (or compositions) that are less corrosive towards tungsten(i.e., in which tungsten etches at a lower rate).

BRIEF SUMMARY OF THE INVENTION

A chemical mechanical polishing composition for polishing a substratehaving a tungsten layer is disclosed. In one embodiment, the polishingcomposition includes a water based liquid carrier, a colloidal silicaabrasive dispersed in the liquid carrier and having a permanent positivecharge of at least 6 mV, an amine containing polymer in solution in theliquid carrier, and an iron containing accelerator. A method forchemical mechanical polishing a substrate including a tungsten layer isfurther disclosed. The method may include contacting the substrate withthe above described polishing composition, moving the polishingcomposition relative to the substrate, and abrading the substrate toremove a portion of the tungsten from the substrate and thereby polishthe substrate.

DETAILED DESCRIPTION OF THE INVENTION

A chemical mechanical polishing composition for polishing a substratehaving a tungsten layer is disclosed. The polishing composition includesa water based liquid carrier, a colloidal silica abrasive dispersed inthe liquid carrier and having a permanent positive charge of at least 6mV, and an amine compound in solution in the liquid carrier. The aminecompound may include substantially any suitable amine compound, forexample, an amine compound including an alkyl group having 12 or morecarbon atoms, a polycationic amine compound, and/or an amine containingpolymer. The polishing composition may further optionally include aniron containing accelerator, such as an iron containing catalyst, astabilizer bound to the iron containing accelerator, a hydrogen peroxideoxidizer, and/or a pH in a range from about 2.0 to about 3.5. Thecolloidal silica may also be treated with an aminosilane compound.

The polishing composition contains an abrasive including colloidalsilica particles which are desirably suspended in a liquid carrier(e.g., water). As used herein the term colloidal silica particles refersto silica particles that are prepared via a wet process rather than apyrogenic or flame hydrolysis process which produces structurallydifferent particles. The colloidal silica particles may be aggregated ornon-aggregated. Non-aggregated particles are individually discreteparticles that may be spherical or nearly spherical in shape, but canhave other shapes as well (such as generally elliptical, square, orrectangular cross-sections). Aggregated particles are particles in whichmultiple discrete particles are clustered or bonded together to formaggregates having generally irregular shapes.

Preferably, the colloidal silica is precipitated orcondensation-polymerized silica, which may be prepared using any methodknown to those of ordinary skill in the art, such as by the sol gelmethod or by silicate ion-exchange. Condensation-polymerized silicaparticles are often prepared by condensing Si(OH)₄ to form substantiallyspherical particles. The precursor Si(OH)₄ may be obtained, for example,by hydrolysis of high purity alkoxysilanes, or by acidification ofaqueous silicate solutions. Such abrasive particles may be prepared, forexample, in accordance with U.S. Pat. No. 5,230,833 or may be obtainedas any of various commercially available products such as the BINDZIL50/80, 30/310, and 40/130 products from EKA Chemicals, the Fuse PL-1,PL-2, PL-3, and PL-3H products, and the Nalco 1034A, 1050, 2327, and2329 products, as well as other similar products available from DuPont,Bayer, Applied Research, Nissan Chemical (the SNOWTEX products), andClariant.

The particle size of a particle is the diameter of the smallest spherethat encompasses the particle. The abrasive particles may have anysuitable particle size. The abrasive particles may have an averageparticle size of about 5 nm or more (e.g., about 10 nm or more, about 15nm or more, about 20 nm or more, or about 30 nm or more). The abrasiveparticles may have an average particle size of about 150 nm or less(e.g., about 130 nm or less, about 80 nm or less, about 50 nm or less,or about 30 nm or less). Accordingly, the abrasive particles may have anaverage particle size in a range from about 10 nm to about 150 nm (e.g.,from about 20 nm to about 130 nm, from about 15 nm to about 100 nm, fromabout 20 nm to about 80 nm, or from about 20 nm to about 60 nm).

The polishing composition may include any suitable amount of colloidalsilica particles. The polishing composition typically includes about0.01 wt. % or more colloidal silica (e.g., about 0.05 wt. % or more).More typically, the polishing composition may include about 0.1 wt. % ormore (e.g., about 1 wt. % or more, about 5 wt. % or more, about 7 wt. %or more, about 10 wt. % or more, or about 12 wt. % or more) colloidalsilica particles. The amount of colloidal silica particles in thepolishing composition is typically about 30 wt. % or less, and moretypically about 20 wt. % or less (e.g., about 15 wt. % or less, about 10wt. % or less, about 5 wt. % or less, about 3 wt. % or less, or about 2wt. % or less). Preferably, the amount of colloidal silica particles inthe polishing composition is in a range from about 0.01 wt. % to about20 wt. %, and more preferably from about 0.05 wt. % to about 15 wt. %(e.g., from about 0.1 wt. % to about 10 wt. %, from about 0.1 wt. % toabout 4 wt. %, from about 0.1 wt. % to about 3 wt. %, from about 0.1 wt.% to about 2 wt. %, or from about 0.2 wt. % to about 2 wt. %).

The liquid carrier is used to facilitate the application of the abrasiveand any optional chemical additives to the surface of a suitablesubstrate to be polished (e.g., planarized). The liquid carrier may beany suitable carrier (e.g., a solvent) including lower alcohols (e.g.,methanol, ethanol, etc.), ethers (e.g., dioxane, tetrahydrofuran, etc.),water, and mixtures thereof. Preferably, the liquid carrier comprises,consists essentially of, or consists of water, more preferably deionizedwater.

The colloidal silica particles have a positive charge of at least 6 mVin the polishing composition. The charge on dispersed particles such ascolloidal silica particles is commonly referred to in the art as thezeta potential (or the electrokinetic potential). The zeta potential ofa particle refers to the electrical potential difference between theelectrical charge of the ions surrounding the particle and theelectrical charge of the bulk solution of the polishing composition(e.g., the liquid carrier and any other components dissolved therein).The zeta potential is typically dependent on the pH of the aqueousmedium. For a given polishing composition, the isoelectric point of theparticles is defined as the pH at which the zeta potential is zero. Asthe pH is increased or decreased away from the isoelectric point, thesurface charge (and hence the zeta potential) is correspondinglydecreased or increased (to negative or positive zeta potential values).The zeta potential of a dispersion such as a polishing composition maybe obtained using commercially available instrumentation such as theZetasizer available from Malvern Instruments, the ZetaPlus ZetaPotential Analyzer available from Brookhaven Instruments, and anelectro-acoustic spectrometer available from Dispersion Technologies,Inc.

The colloidal silica particles in the polishing composition have apermanent positive charge of about 6 mV or more (e.g., about 10 mV ormore, about 15 mV or more, about 20 mV or more, about 25 mV or more, orabout 30 mV or more). The colloidal silica particles in the polishingcomposition may have a permanent positive charge of about 50 mV or less(e.g., about 45 mV or less, about 40 mV or less, or about 35 mV orless). Preferably, the colloidal silica particles have a permanentpositive charge in a range from about 6 mV to about 50 mV (e.g., about10 mV to about 45 mV, about 15 mV to about 40 mV, or about 20 mV toabout 40 mV).

By permanent positive charge it is meant that the positive charge on thesilica particles is not readily reversible, for example, via flushing,dilution, filtration, and the like. A permanent positive charge may bethe result, for example, of covalently bonding a cationic compound withthe colloidal silica. A permanent positive charge is in contrast to areversible positive charge that may be the result, for example, of anelectrostatic interaction between a cationic compound and the colloidalsilica.

Notwithstanding, as used herein, a permanent positive charge of at least6 mV means that the zeta potential of the colloidal silica particlesremains above 6 mV after the following three step ultrafiltration test.A volume of the polishing composition (e.g., 200 ml) is passed through aMillipore Ultracell regenerated cellulose ultrafiltration disk (e.g.,having a MW cutoff of 100,000 Daltons and a pore size of 6.3 nm). Theremaining dispersion (the dispersion that is retained by theultrafiltration disk) is collected and replenished to the originalvolume with pH adjusted deionized water. The deionized water is pHadjusted to the original pH of the polishing composition using asuitable inorganic acid such as nitric acid. This procedure is repeatedfor a total of three ultrafiltration cycles (each of which includes anultrafiltration step and a replenishing step). The zeta-potential of thetriply ultra-filtered and replenished polishing composition is thenmeasured and compared with the zeta potential of the original polishingcomposition. This three step ultrafiltration test is further illustratedbelow by way of example (in Example 5).

While not wishing to be bound by theory, it is believed that thedispersion retained by the ultrafiltration disk (the retaineddispersion) includes the colloidal silica particles and any chemicalcompounds (e.g., cationic compounds) that may be associated with thesurface of the particles (e.g., bonded or attached to orelectrostatically interacting with the particle surface). At least aportion of the liquid carrier and the chemical compounds dissolvedtherein pass through the ultrafiltration disk. Replenishing the retaineddispersion to the original volume is believed to upset the equilibriumin the original polishing composition such that the chemical compoundsassociated with the particle surface may tend towards a new equilibrium.Compounds that are strongly associated (e.g., covalently bonded) withthe particle surface remain on the surface such that there tends to belittle if any change in the positive zeta potential of the particle. Incontrast, a portion of compounds that have a weaker association (e.g.,an electrostatic interaction) with the particle surface may return tothe solution as the system tends towards the new equilibrium therebyresulting in a reduction in the positive zeta potential. Repeating thisprocess for a total of three ultrafiltration and replenishing cycles isbelieved to amplify the above described effect.

It is preferred that after correcting for ionic strength differencesthere is little (or no) difference between the zeta potential of thecolloidal silica particles in the original polishing composition and theparticles in the triply ultra-filtered and replenished polishingcomposition obtained from the above described three step ultrafiltrationtest. It will be understood that prior to correcting for ionic strengthdifferences, the measured zeta potential may be observed to increase dueto the reduced ionic strength (owing to dilution) of the triplyultra-filtered and replenished polishing composition. After correctingfor ionic strength differences, it is preferred that any reduction inthe positive charge (reduction in the positive zeta potential) on theparticles resulting from the aforementioned three step ultrafiltrationtest is less than 10 mV (e.g., less than about 7 mV, less than about 5mV, or even less than about 2 mV).

The polishing composition is generally acidic having a pH of less thanabout 7. The polishing composition typically has a pH of about 1 or more(e.g., about 1.5 or more, or about 2 or more). Preferably, the polishingcomposition has a pH of about 6 or less (e.g., about 5 or less, or about4 or less). More preferably, the polishing composition has a pH in arange from about 1 to about 6 (e.g., from about 1.5 to about 5, or fromabout 2 to about 4, or from about 2 to about 3.5). The pH of thepolishing composition may be achieved and/or maintained by any suitablemeans. The polishing composition may include substantially any suitablepH adjusting agents or buffering systems. For example, suitable pHadjusting agents may include nitric acid, sulfuric acid, phosphoricacid, phthalic acid, citric acid, adipic acid, oxalic acid, malonicacid, maleic acid, ammonium hydroxide, and the like while suitablebuffering agents may include phosphates, sulfates, acetates, malonates,oxalates, borates, ammonium salts, and the like.

Colloidal silica particles having a permanent positive charge in thepolishing composition may be achieved, for example, via treating theparticles with at least one aminosilane compound. Such compounds includeprimary aminosilanes, secondary aminosilanes, tertiary aminosilanes,quaternary aminosilanes, and multi-podal (e.g., dipodal) aminosilanes.The aminosilane compound can be any suitable aminosilane, such asbis(2-hydroxyethyl)-3-aminopropyl trialkoxysilane,diethylaminomethyltrialkoxysilane,(N,N-diethyl-3-aminopropyl)trialkoxysilane),3-(N-styrylmethyl-2-aminoethylaminopropyl trialkoxysilane, aminopropyltrialkoxysilane, (2-N-benzylaminoethyl)-3-aminopropyl trialkoxysilane),trialkoxysilyl propyl-N,N,N-trimethyl ammonium chloride,N-(trialkoxysilylethyl)benzyl-N,N,N-trimethyl ammonium chloride,(bis(methyldialkoxysilylpropyl)-N-methyl amine,bis(trialkoxysilylpropyl)urea,bis(3-(trialkoxysilyl)propyl)-ethylenediamine,bis(trialkoxysilylpropyl)amine, bis(trialkoxysilylpropyl)amine, andmixtures thereof.

Any suitable method of treating the colloidal silica particles, many ofwhich are known to those of ordinary skill in the art may be used. Forexample, the colloidal silica particles may be treated with theaminosilane compound before mixing with the other components of thepolishing composition or the aminosilane and the colloidal silicaparticles may be added simultaneously to the other components of thepolishing composition.

The aminosilane compound may be present in the polishing composition inany suitable amount. The amount of aminosilane utilized may depend onseveral factors, for example, including the particle size, the surfacearea of the particle, the particular aminosilane compound used, and thedesired charge on the particle. In general the amount of aminosilaneused increases with decreasing particle size (and therefore increasingsurface area) and increasing charge on the particle. For example, toachieve a permanent positive charge of 25 mV or more, 20 ppm or more ofaminosilane may be used for a dispersion having a particle size of 110nm, 70 ppm or more of aminosilane may be used for a dispersion having aparticle size of 75 nm, and 130 ppm or more of aminosilane may be usedfor a dispersion having a particle size of 55 nm. Thus the polishingcomposition may include about 5 ppm or more (e.g., about 10 ppm or more,about 15 ppm or more, or about 20 ppm or more) of the aminosilanecompound. The polishing composition preferably includes an amount ofaminosilane sufficient to provide the desired permanent positive chargewithout using an excess. Thus the polishing composition may includeabout 500 ppm or less (e.g., about 300 ppm or less, or about 200 ppm orless, or about 150 ppm or less) of the aminosilane compound. Preferably,the polishing composition includes a range from about 5 ppm to about 500ppm (e.g., from about 10 ppm to about 300 ppm, from about 15 ppm toabout 200 ppm, or from about 20 ppm to about 150 ppm) of the aminosilanecompound.

Optional embodiments of the polishing composition may further include aniron containing accelerator. An iron containing accelerator as usedherein is an iron containing chemical compound that increases theremoval rate of tungsten during a tungsten CMP operation. For example,the iron containing accelerator may include an iron containing catalystsuch as is disclosed in U.S. Pat. Nos. 5,958,288 and 5,980,775. Such aniron containing catalyst may be soluble in the liquid carrier and mayinclude, for example, ferric (iron III) or ferrous (iron II) compoundssuch as iron nitrate, iron sulfate, iron halides, including fluorides,chlorides, bromides, and iodides, as well as perchlorates, perbromatesand periodates, and organic iron compounds such as iron acetates,acetylacetonates, citrates, gluconates, malonates, oxalates, phthalates,and succinates, and mixtures thereof.

An iron containing accelerator may also include an iron containingactivator (e.g., a free radical producing compound) or an ironcontaining catalyst associated with (e.g., coated or bonded to) thesurface of the colloidal silica particle such as is disclosed in U.S.Pat. Nos. 7,029,508 and 7,077,880. For example, the iron containingaccelerator may be bonded with the silanol groups on the surface of thecolloidal surface particle. In one embodiment the iron containingaccelerator may include a boron containing stabilizer and an ironcontaining catalyst. In such embodiments the stabilizer and catalyst mayoccupy substantially any percentage of the available surface sites onthe colloidal silica particles, for example, greater than 1%, greaterthan 50%, or greater than 80% of the available surface sites.

The amount of iron containing accelerator in the polishing compositionmay be varied depending upon the oxidizing agent used and the chemicalform of the accelerator. When the preferred oxidizing agent hydrogenperoxide (or its analogs) is used and a soluble iron containing catalystis used (such as ferric nitrate), the catalyst may be present in thecomposition in an amount sufficient to provide a range from about 1 toabout 3000 ppm Fe based on the total weight of the composition. Thepolishing composition preferably includes about 1 ppm Fe or more (e.g.,about 5 ppm or more, about 10 ppm or more, or about 20 ppm or more). Thepolishing composition preferably includes about 500 ppm Fe or less(e.g., about 200 ppm or less, about 100 ppm or less, or about 50 ppm orless). The polishing composition may thus include a range from about 1to about 500 ppm Fe (e.g., from about 3 to about 200 ppm, from about 5to about 100 ppm, or from about 10 to about 50 ppm).

Embodiments of the polishing composition including an iron containingaccelerator may further include a stabilizer. Without such a stabilizer,the iron containing accelerator and the oxidizing agent may react in amanner that degrades the oxidizing agent rapidly over time. The additionof a stabilizer tends to reduce the effectiveness of the iron containingaccelerator such that the choice of the type and amount of stabilizeradded to the polishing composition may have a significant impact on CMPperformance. The addition of a stabilizer may lead to the formation of astabilizer/accelerator complex that inhibits the accelerator fromreacting with the oxidizing agent while at the same time allowing theaccelerator to remain sufficiently active so as to promote rapidtungsten polishing rates.

Useful stabilizers include phosphoric acid, organic acids, phosphonatecompounds, nitriles, and other ligands which bind to the metal andreduce its reactivity toward hydrogen peroxide decomposition and mixturethereof. The acid stabilizers may be used in their conjugate form, e.g.,the carboxylate can be used instead of the carboxylic acid. For purposesof this application the term “acid” as it is used to describe usefulstabilizers also means the conjugate base of the acid stabilizer. Forexample the term “adipic acid” means adipic acid and its conjugate base.Stabilizers can be used alone or in combination and significantlydecrease the rate at which oxidizing agents such as hydrogen peroxidedecomposes.

Preferred stabilizers include phosphoric acid, phthalic acid, citricacid, adipic acid, oxalic acid, malonic acid, aspartic acid, succinicacid, glutaric acid, pimelic acid, suberic acid, azelaic acid, sebacicacid, maleic acid, glutaconic acid, muconic acid,ethylenediaminetetraacetic acid (EDTA), propylenediaminetetraacetic acid(PDTA), and mixtures thereof. The preferred stabilizers may be added tothe compositions and slurries of this invention in an amount rangingfrom about 1 equivalent per iron containing accelerator to about 3.0weight percent or more. As used herein, the term “equivalent per ironcontaining accelerator” means one molecule of stabilizer per iron ion inthe composition. For example 2 equivalents per iron containingaccelerator means two molecules of stabilizer for each catalyst ion.

The polishing composition may further include an oxidizing agent. Theoxidizing agent may be added to the polishing composition during theslurry manufacturing process or just prior to the CMP operation (e.g.,in a tank located at the semiconductor fabrication facility). Preferableoxidizing agents include inorganic or organic per-compounds. Aper-compound as defined by Hawley's Condensed Chemical Dictionary is acompound containing at least one peroxy group (—O—O—) or a compoundcontaining an element in its highest oxidation state. Examples ofcompounds containing at least one peroxy group include but are notlimited to hydrogen peroxide and its adducts such as urea hydrogenperoxide and percarbonates, organic peroxides such as benzoyl peroxide,peracetic acid, and di-t-butyl peroxide, monopersulfates (SO₅ ⁻),dipersulfates (S₂O₈ ⁻), and sodium peroxide. Examples of compoundscontaining an element in its highest oxidation state include but are notlimited to periodic acid, periodate salts, perbromic acid, perbromatesalts, perchloric acid, perchlorate salts, perboric acid, and perboratesalts and permanganates. The most preferred oxidizing agents is hydrogenperoxide.

The oxidizing agent may be present in the polishing composition in anamount ranging, for example, from about 0.1 to about 10 weight percent.In preferred embodiments in which a hydrogen peroxide oxidizer and asoluble iron containing accelerator are used, the oxidizer may bepresent in the polishing composition in an amount ranging from about 0.1to about 6 weight percent (e.g., from about 0.2 to about 5 weightpercent, from about 0.5 to about 4 weight percent, or from about 1 toabout 3 weight percent).

The polishing composition further includes an amine compound in solutionin the liquid carrier. The amine compound may include substantially anyamine compound that inhibits tungsten etching (i.e., reduces tungstenetch rates) in the presence of an oxidizer such as hydrogen peroxide.The addition of an amine compound may also have a negative impact on CMPperformance. Thus the amine compound may be selected such that itadvantageously inhibits tungsten etching while at the same time allowingfor high tungsten removal rates during the CMP operation. The aminecompound (or compounds) may include a primary amine, a secondary amine,a tertiary amine, or a quaternary amine. The amine compound may furtherinclude a monoamine, a diamine, a triamine, a tetramine, or an aminebased polymer having a large number of repeating amine groups (e.g., 4or more amine groups).

In certain embodiments of the polishing compound the amine compound mayinclude a long chain alkyl group. By long chain alkyl group it is meantthat the amine compound includes an alkyl group having at least 10carbon atoms (e.g., at least 12 carbon atoms or at least 14 carbonatoms). Such amine compounds may include, for example, dodecylamine,tetradecylamine, hexadecylamine, octadecylamine, oleylamine,N-methyldioctylamine, N-methyloctadecylamine, cocamidopropylamine oxide,benzyldimethylhexadecylammonium chloride, benzalkonium chloride,cocoalkylmethyl[polyoxyethylene (15)]ammonium chloride,octadecylmethyl[polyoxyethylene (15)]ammonium chloride,cetyltrimethylammonium bromide, and the like.

In certain embodiments of the polishing composition the amine compoundmay include a polycationic amine. A polycationic amine (as the term isused herein) is an amine compound having multiple (two or more) aminegroups in which each of the amine groups is cationic (i.e., has apositive charge). Thus the polycationic amine may include apolyquaternary amine. By polyquaternary amine it is meant that the aminecompound includes from 2 to 4 quaternary ammonium groups such that thepolyquaternary amine is a diquaternary amine, a triquaternary amine, ora tetraquaternary amine compound. Diquaternary amine compounds mayinclude, for example, N,N′-methylenebis(dimethyltetradecylammoniumbromide), 1,1,4,4-tetrabutylpiperazinediium dibromide,N,N,N′,N′,N′-pentamethyl-N-tallow-1,3-propane-diammonium dichloride,N,N′-hexamnethylenebis(tributylammonium hydroxide), decamethoniumbromide, didodecyl-tetramethyl-1,4-butanediaminium diiodide,1,5-dimethyl-1,5-diazoniabicyclo(3.2.2)nonane dibromide, and the like.Triquaternary amine compounds may include, for example,N(1),N(6)-didoecyl-N(1),N(1),N(6),N(6)-tetramethyl-1,6-hexanediaminiumdiiodide. Tetraquaternary amine compounds may include, for example,methanetetrayltetrakis(tetramethylammonium bromide). The polyquaternaryamine compound may further include a long chain alkyl group (e.g.,having 10 or more carbon atoms). For example, a polyqyaternary aminecompound having a long chain alkyl group may include N,N′-methylenebis(dimethyltetradecylammonium bromide),N,N,N′,N′,N′-pentamethyl-N-tallow-1,3-propane-diammonium dichloride,didodecyl-tetramethyl-1,4-butanediaminium diiodide, andN(1),N(6)-didodecyl-N(1),N(1),N(6),N(6)-tetramethyl-1,6-hexanediaminiumdiiodide.

A polycationic amine may also be polycationic in that each of the aminegroups is protonated (and therefore has a positive charge). For example,a dicationic amine such as tetramethyl-p-phenylenediamine includes twotertiary amine groups that may be protonated (and therefore positivelycharged) at polishing composition pH values less than the pKa of theamine compound.

In certain embodiments of the polishing composition the amine compoundmay include an amine based polymer. Such a polymer includes four or moreamine groups. The amine based polymer may include, for example,triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, andpolymers including the following amine containing functional groupsmethacryloylox-ethyl trimethyl ammonium methylsulfate, diallyl dimethylammonium chloride, and methacrylamido-propyl trimethyl ammoniumchloride.

It will be understood that the amine compound does not include aheterocyclic polyamine. Heterocyclic polyamines are amine compoundshaving multiple amine groups in which at least one of the amine groupsis located in a ring (e.g., a ring including 3, 4, 5, 6, 7, or 8members). Such heterocyclic amine compounds include, for example,certain pyridine, pyridylamine, pyrimidine, and azole compounds. Whilesuch heterocyclic polyamines (such as benzotriazole) are knowninhibitors of copper etching, their utility in inhibiting tungstenetching tends to be limited. As such they are not particularly useful inthe disclosed tungsten CMP compositions.

The polishing composition may include substantially any suitableconcentration of the amine compound. In general the concentration isdesirably high enough to provide adequate etch inhibition, but lowenough so that the compound is soluble and so as not to reduce tungstenpolishing rates below acceptable levels. By soluble it is meant that thecompound is fully dissolved in the liquid carrier or that it formsmicelles in the liquid carrier or is carried in micelles. It may benecessary to vary the concentration of the amine compound depending uponnumerous various factors, for example, including the solubility of theamine compound, the number of amine groups in the amine compound, thelength of an alkyl group in the amine compound, the relationship betweenetch rate inhibition and polishing rate inhibition, the oxidizing agentused, the concentration of the oxidizing agent, and so on. In certaindesirable embodiments, the concentration of the amine compound in thepolishing composition is in a range from about 0.1 μM to about 10 mM(i.e., from about 10⁻⁷ to about 10⁻² molar). For example, in embodimentsutilizing an amine based polymer having a high molecular weight, theconcentration may be on the lower end of the range (e.g., from about10⁻⁷ to about 10⁻⁴ molar). In other embodiments utilizing acomparatively simple amine compound (having fewer amine groups and alower molecular weight), the concentration may be on the higher end ofthe range (e.g., from about 10⁻⁵ to about 10⁻² molar).

The polishing composition may optionally further include a biocide. Thebiocide may include any suitable biocide, for example an isothiazolinonebiocide. The amount of biocide in the polishing composition typically isin a range from about 1 ppm to about 50 ppm, and preferably from about 1ppm to about 20 ppm.

The polishing composition may be prepared using any suitable techniques,many of which are known to those skilled in the art. The polishingcomposition may be prepared in a batch or continuous process. Generally,the polishing composition may be prepared by combining the componentsthereof in any order. The term “component” as used herein includes theindividual ingredients (e.g., the colloidal silica, the iron containingaccelerator, the amine compound, etc.)

For example, the silica may be dispersed in the aqueous liquid carrier.The silica may then be treated, for example, with an aminosilane so asto produce generate a colloidal silica having a permanent positivecharge of at least 6 mV. Other components such as an iron containingaccelerator, a stabilizer, and the amine compound may then be added andmixed by any method that is capable of incorporating the components intothe polishing composition. The oxidizing agent may be added at any timeduring the preparation of the polishing composition. For example, thepolishing composition may be prepared prior to use, with one or morecomponents, such as the oxidizing agent, being added just prior to theCMP operation (e.g., within about 1 minute, or within about 10 minutes,or within about 1 hour, or within about 1 day, or within about 1 week ofthe CMP operation). The polishing composition also may also be preparedby mixing the components at the surface of the substrate (e.g., on thepolishing pad) during the CMP operation.

The polishing composition may be supplied as a one-package systemcomprising a colloidal silica having a permanent positive charge of atleast 6 mV, an amine compound, an optional iron containing acceleratorand stabilizer, an optional biocide, and water. The oxidizing agentdesirably is supplied separately from the other components of thepolishing composition and is combined. e.g., by the end-user, with theother components of the polishing composition shortly before use (e.g.,1 week or less prior to use, 1 day or less prior to use, 1 hour or lessprior to use, 10 minutes or less prior to use, or 1 minute or less priorto use). Various other two-container, or three- or more-container,combinations of the components of the polishing composition are withinthe knowledge of one of ordinary skill in the art.

The polishing composition of the invention may also be provided as aconcentrate which is intended to be diluted with an appropriate amountof water prior to use. In such an embodiment, the polishing compositionconcentrate may include the colloidal silica having a permanent positivecharge of at least 6 mV, the amine compound, the optional ironcontaining accelerator and stabilizer, the optional biocide, and water,with or without the oxidizing agent, in amounts such that, upon dilutionof the concentrate with an appropriate amount of water, and theoxidizing agent if not already present in an appropriate amount, eachcomponent of the polishing composition will be present in the polishingcomposition in an amount within the appropriate range recited above foreach component. For example, the colloidal silica having a permanentpositive charge of at least 6 mV, the amine compound, the optional ironcontaining accelerator and the stabilizer, may each be present in thepolishing composition in an amount that is about 2 times (e.g., about 3times, about 4 times, about 5 times, or even about 10 times) greaterthan the concentration recited above for each component so that, whenthe concentrate is diluted with an equal volume of (e.g., 2 equalvolumes of water, 3 equal volumes of water, 4 equal volumes of water, oreven 9 equal volumes of water respectively), along with the oxidizingagent in a suitable amount, each component will be present in thepolishing composition in an amount within the ranges set forth above foreach component. Furthermore, as will be understood by those of ordinaryskill in the art, the concentrate may contain an appropriate fraction ofthe water present in the final polishing composition in order to ensurethat other components are at least partially or fully dissolved in theconcentrate.

Although the polishing composition of the invention may be used topolish any substrate, the polishing composition is particularly usefulin the polishing of a substrate comprising at least one metal includingtungsten and at least one dielectric material. The tungsten layer may bedeposited over one or more barrier layers, for example, includingtitanium and/or titanium nitride (TiN). The dielectric layer may be ametal oxide such as a silicon oxide layer derived fromtetraethylorthosilicate (TEOS), porous metal oxide, porous or non-porouscarbon doped silicon oxide, fluorine-doped silicon oxide, glass, organicpolymer, fluorinated organic polymer, or any other suitable high orlow-k insulating layer.

The polishing method of the invention is particularly suited for use inconjunction with a chemical mechanical polishing (CMP) apparatus.Typically, the apparatus includes a platen, which, when in use, is inmotion and has a velocity that results from orbital, linear, or circularmotion, a polishing pad in contact with the platen and moving with theplaten when in motion, and a carrier that holds a substrate to bepolished by contacting and moving relative to the surface of thepolishing pad. The polishing of the substrate takes place by thesubstrate being placed in contact with the polishing pad and thepolishing composition of the invention and then the polishing pad movingrelative to the substrate, so as to abrade at least a portion of thesubstrate (such as tungsten, titanium, titanium nitride, and/or adielectric material as described herein) to polish the substrate.

A substrate can be planarized or polished with the chemical mechanicalpolishing composition with any suitable polishing pad (e.g., polishingsurface). Suitable polishing pads include, for example, woven andnon-woven polishing pads. Moreover, suitable polishing pads can compriseany suitable polymer of varying density, hardness, thickness,compressibility, ability to rebound upon compression, and compressionmodulus. Suitable polymers include, for example, polyvinylchloride,polyvinylfluoride, nylon, fluorocarbon, polycarbonate, polyester,polyacrylate, polyether, polyethylene, polyamide, polyurethane,polystyrene, polypropylene, coformed products thereof, and mixturesthereof.

The following examples further illustrate the invention but, of course,should not be construed as in any way limiting its scope.

Example 1

A number of polishing compositions were prepared in order to evaluatevarious performance metrics of the compositions. A standard compositionwas used as a base composition for all formulations with only the amountand type of amine compound varied. The standard composition was preparedas follows:

A dispersion was prepared including 3.0 weight percent colloidal silicaand 0.01 weight percent (100 ppm) ofbis-(gamma-trimethoxysilylpropyl)amine (an aminosilane). The dispersionwas prepared by mixing a concentrated colloidal silica dispersion havinga mean particle size of 75 nm (such as are commercially available fromAkso Nobel, Fuso, and Nalco as listed above) with the aminosilane andwater. The dispersion was mixed for a number of hours to adequatelytreat the colloidal silica with the aminosilane. The treated colloidalsilica dispersion was then added to a mixture including malonic acid,ferric nitrate, and water such that the final concentrations in thecomposition were as follows: 2.0 weight percent treated colloidalsilica, 0.0031 weight percent feric nitrate, and 0.067 weight percentmalonic acid. The pH of the mixture was then adjusted to 2.4 usingnitric acid. This mixture was used as a stock solution in which variousamine compounds were dissolved prior to performing zeta potentialmeasurements, static etch tests, and CMP tests as described in moredetail in the subsequent examples.

Example 2

The tungsten etch rate and zeta potential of the colloidal silica wereevaluated in this example for various polishing compositions. Thisexample demonstrates the effect of various amine compounds as a functionof the longest alkyl chain length in the amine compound. To obtain thetungsten etch rate for each polishing composition, the composition wasfirst heated to 45 degrees C. after which hydrogen peroxide was added toa concentration of 2 percent. After waiting 5 minutes for thetemperature to return to 45 degrees, a two-inch wafer having a tungstenlayer was submersed in the polishing compositions for 5 minutes.Tungsten removal rates were determined via resistivity measurements madebefore and after immersion in the polishing compositions. The zetapotential measurements were obtained using a DT1200 electro-acousticspectrometer available from Dispersion Technologies, Inc. The polishingcompositions (Controls A and B and inventive compositions 2A through 2M)were obtained by adding an appropriate amount of the indicated aminecompound to a sample of the stock solution described above in Example 1.The alkyl chain length (in number of carbon atoms), the concentration ofthe amine compound, the tungsten etch rate, and the zeta potential ofthe colloidal silica particles are indicated in Table 1. Control Aincluded no inhibitor and control B included glycine. Inventive samples2A through 2M included the following amine compounds: (2A)octadecylmethyl[polyoxyethylene (15)] ammonium chloride, (2B)cocoalkylmethyl[polyoxyethylene (15)] ammonium chloride, (2C)benzalkonium chloride, (2D) hexadecylamine, (2E)benzyldimethylhexadecylammonium chloride, (2F) tetradecylamine, (2G)dodecylamine, (2H) decylamine, (2I) octylamine, (2J) cocamidopropylamineoxide, (2K) benzyltributylammonium chloride, and (2L) tetrabutylammoniumhydroxide.

TABLE 1 Polishing Alkyl Chain Concentra- W Etch Rate Zeta Poten-Composition Length (#C) tion (mmol) (Ang/min) tial (mV) Control A 132Control B 2 2.4 78 26 2A 18 2.4 11 27 1.2 9 2B 16 2.4 4 27 2C 16 2.4 934 1.2 6 2D 16 2.4 4 26 1.2 1 2E 14 2.4 4 33 1.2 4 2F 14 2.4 2 28 1.2 112G 12 2.4 5 26 1.2 113 2H 10 2.4 140 26 1.2 134 2I 8 2.4 115 25 1.2 1422J 4 2.4 2 32 1.2 3 2K 4 2.4 132 30 1.2 160 2L 4 2.4 143 30 1.2 124

As is apparent from the results set forth in Table 1, compositions2A-2G, which included amine compounds having an alkyl chain lengthgreater than 10 (12, 14, 16, and 18) exhibited W etch rates of one-tenthor less that of control A (no inhibitor) and one-seventh or less that ofcontrol B (glycine).

Example 3

The tungsten etch rate and zeta potential of the colloidal silica wereevaluated in this example for various other polishing compositions. Thisexample demonstrates the effect of various amine containing polymers(3A-3E). The tungsten etch rates and zeta potential measurements wereobtained using the same methodologies as described in Example 2. Thepolishing compositions (controls A and B and inventive compositions 3Athrough 3E) were obtained by adding an appropriate amount of theindicated amine compound to a sample of the stock solution describedabove in Example 1. The alkyl chain length (in number of carbon atoms),the concentration of the amine compound, the tungsten etch rate, and thezeta potential of the colloidal silica are indicated in Table 2. ControlA included no inhibitor and control B included glycine. Inventivesamples 3A through 3E included the following amine compounds: (3A)Merquat 280 which is a polymer having alternating diallyl dimethylammonium chloride and acrylic acid groups and having a molecular weightof about 450,000, (3B) Merquat 106 which is a polymer having repeatingdimethyl ammonium chloride groups and a molecular weight of about15,000, (3C) pentaethylenehexamine, (3D) tetraethylenepentamine, and(3E) pentamethyldiethylenetriamine.

TABLE 2 Polishing Alkyl Chain Concentra- W Etch Rate Zeta Poten-Composition Length (#C) tion (mmol) (Ang/min) tial (mV) Control A 132Control B 2 2.4 78 26 3A 4 0.0012 20 NA 0.00062 28 3B 4 0.0012 54 NA0.00062 48 3C 4 2.4 51 23 1.2 44 3D 2 2.4 54 22 1.2 38 3E 2 2.4 132 241.2 125

As is apparent from the results set forth in Table 2, compositions 3A,3B, 3C, and 3D exhibited W etch rates significantly less than that ofthe controls. The etch rate of composition 3E was similar to that ofcontrol A (no inhibitor).

Example 4

The tungsten etch rate and zeta potential of the colloidal silica wereevaluated in this example for still other polishing compositions. Thisexample demonstrates the effect of various polycationic amine containingcompounds (4A-4K). The tungsten etch rates and zeta potentialmeasurements were obtained using the same methodologies as described inExample 2. The polishing compositions (controls A and B and inventivecompositions 4A through 4K) were obtained by adding an appropriateamount of the indicated amine compound to a sample of the stock solutiondescribed above in Example 1. The alkyl chain length (in number ofcarbon atoms), the concentration of the amine compound, the tungstenetch rate, and the zeta potential of the colloidal silica are indicatedin Table 3. Control A included no inhibitor and control B includedglycine. Inventive samples 4A through 4K included the following aminecompounds: (4A) N,N′-methylenebis (dimethyltetradecylammonium bromide),(4B) 1,1,4,4-tetrabutylpiperazinedium dibromide, (4C)N,N,N′,N′,N′-pentamethyl-N-tallow-1,3-propane-diammonium dichloride,(4D) 1,5-dimethyl-1,5-diazoniabicyclo(3.2.2)nonane dibromide, (4E)N(1),N(6)-didoecyl-N(1),N(1),N(6),N(6)-tetramethyl-1,6-hexanediaminiumdiiodide, (4F) decamethonium bromide, (4G)methanetetrayltetrakis(tetramethylammonium bromide), (4H) hexamethoniumchloride, (4I) tetramethyl-p-phenylenediamine, (4J)didodecyl-tetramethyl-1,4-butanediaminium diiodide, and (4K) N(1), N(1),N(3)-tributyl-N(3)-{3-[dibutyl(methyl)ammonio]propyl-N(1),N(3)-dimethyl-1,3-propanediaminium triiodide.

TABLE 3 Polishing Alkyl Chain Concentra- W Etch Rate Zeta Poten-Composition Length (#C) tion (mmol) (Ang/min) tial (mV) Control A 132Control B 2 2.4 78 26 4A 10 0.6 4 28 0.3 14 4B 4 0.6 78 27 0.3 48 4C 180.2 11 25 0.1 57 4D 3 0.6 19 27 0.3 6 4E 12 0.6 −2 27 0.3 121 4F 3 0.6116 29 0.3 113 4G 5 0.6 110 29 0.3 121 4H 6 2.4 185 30 1.2 176 4I 1 2.4102 25 1.2 117 4J 12 0.6 0 29 0.3 0 4K 4 0.6 19 29 0.3 121

As is apparent from the results set forth in Table 3, compositions 4A,4C, 4D, 4E, 4J, and 4K may exhibit W etch rates significant less thanthat of the controls (depending on the concentration of the inhibitor).

Example 5

The tungsten etch rate and zeta potential of the colloidal silica wereevaluated in this example for various other polishing compositions. Thisexample demonstrates the effect of various heterocyclic polyaminecompounds. The tungsten etch rates and zeta potential measurements wereobtained using the same methodologies as described in Example 2. Thepolishing compositions (controls A and B and compositions 5A through 5F)were obtained by adding an appropriate amount of the indicated aminecompound to a sample of the stock solution described above in Example 1.The alkyl chain length (in number of carbon atoms), the concentration ofthe amine compound, the tungsten etch rate, and the zeta potential ofthe colloidal silica are indicated in Table 4. Control A included noinhibitor and control B included glycine. Samples 5A through 5F includedthe following amine compounds: (5A) 2-(aminomethyl)pyridine, (5B)2,2′dipyridylamine, (5C) benzotriazole, (5D) 2 aminopyrimidine, (5E)4-aminopyridine, and (5F) 5-aminotetrazole.

TABLE 4 Polishing Alkyl Chain Concentra- W Etch Rate Zeta Poten-Composition Length (#C) tion (mmol) (Ang/min) tial (mV) Control A 132Control B 2 2.4 78 26 5A 1 2.4 121 23 1.2 128 5B 0 2.4 99 24 1.2 125 5C0 2.4 174 28 1.2 223 5D 0 2.4 190 28 1.2 115 5E 0 2.4 193 25 1.2 203 5F0 2.4 177 28 1.2 202

As is apparent from the results set forth in Table 4, none ofcompositions 5A through 5F exhibited a W etch rate of less than that ofthe glycine control. All but composition 5B exhibited W etch rates aboutequal to or greater than the control including no inhibitor.

Example 6

Zeta potential measurements and conductivity measurements were obtainedfor treated silica samples before and after filtration. A 200 ml volumeof each composition was filtered through a Millipore Ultracellregenerated cellulose ultrafiltration disk (having a MW cutoff of100.00) Daltons and a pore size of 6.3 nm). The remaining dispersion(the dispersion that was retained by the ultrafiltration disk) wascollected and replenished to the original 200 ml volume using deionizedwater adjusted to pH 2.6 with nitric acid. This procedure was repeatedfor a total of three ultrafiltration cycles (each of which includes anultrafiltration step and a replenishing step). The zeta-potential andelectrical conductivity of the polishing composition were measuredbefore and after the ultrafiltration procedure (i.e., on the originalpolishing composition and the triply ultra-filtered and replenishedpolishing composition). Table 5 shows the measured zeta potential andconductivity for polishing compositions 6A and 6B. Polishing composition6A contained a 55 nm colloidal silica treated with3-(aminopropyl)trimethoxylsilane while polishing composition 6Bcontained a 55 nm colloidal silica treated with tetrabutylammoniumhydroxide. As described above, the zeta potential and electricalconductivity of the original compositions were measured before and afterabove described ultrafiltration procedure. Corrected zeta-potentialvalues of the triply ultra-filtered and replenished polishingcomposition (corrected for ionic strength differences as indicated bythe conductivity change) are also shown.

TABLE 5 Zeta Conduc- Zeta Conduc- Zeta Potential tivity Potential tivityPotential Polishing Before Before After After Corrected Composition (mV)(μs/cm) (mV) (μs/cm) (mV) 6A 41 2130 56 1156 41 6B 10 1030 3 1083 3

As is apparent from the results set forth in Table 5, the zeta potentialof sample 6A is not changed by filtration indicating that the colloidalsilica has a permanent positive charge of 41 mV. The zeta potential ofsample 6B decreased from 10 to 3 mV indicating that the positive chargecolloidal silica was not permanent.

Example 7

Both the tungsten etch rate and the tungsten polishing rate wereevaluated in this example for various polishing compositions. Thisexample demonstrates the effect of various amine compounds on thetungsten etch rates and tungsten polishing rates for the correspondingpolishing compositions. The CMP compositions were obtained using theprocedure described in Example 1. The compositions were similar to thosedescribed above with the exception that they included the followingfinal concentrations: 1.5 weight percent treated colloidal silica,0.0012 weight percent ferric nitrate, 0.0267 weight percent malonicacid, and 0.5 percent hydrogen peroxide.

The tungsten etch rates were obtained using the same methodologydescribed in Example 2. The tungsten polishing rates were obtained usinga Mirra® CMP Tool (available from Applied Materials). Eight inch wafershaving a tungsten layer deposited on a surface thereof were polished onan IC 1010 polishing pad at a down-force of 1.5 psi, a platen speed of100 rpm, and a slurry flow rate of 150 ml/min. The polishingcompositions (the control and compositions 6A through 61) were obtainedby adding an appropriate amount of the indicated amine compound to asample of the stock solution described above in Example 1. The alkylchain length (in number of carbon atoms), the concentration of the aminecompound (in ppm by weight), the tungsten etch rate, and the tungstenpolishing rate are indicated in Table 6. The control included glycine.Samples 6A through 61 included the following amine compounds (6A)N,N,N″,N″-Tetrabutyl-1,6-hexanediamine, (6B) cetyltrimethylammoniumbromide, (6C) Di(hydrogenated Tallowalkyl) quaternary amine, (6D)N,N,N′,N′,N′-pentamethyl-N-tallow-1,3-propane-diammonium dichloride,(6E) poly[(3-(methacryloylamino)-propyl]trimethylammonium chloride,acrylamine and acrylic acid, (6F) an ampholytic terpolymer ofmethacryl-midopropyl trimethyl ammonium chloride, acrylamide and acrylicacid, (6G) polyethylenimine, (6H) Pentamethyldiethylenetriamine, and(6I) 1 [Bis[3-(dimethylamino)propyl]amino]-propanol.

TABLE 6 Polishing Alkyl Chain Concentra- W Etch Rate W Polish RateComposition Length (#C) tion (ppm) (Ang/min) (Ang/min) Control 2 1600 66215 6A 6 1000 63 202 6B 16 100 3 141 50 2 171 6C 18 100 72 79 300 2 736D 18 100 14 138 6E 3 100 110 212 6F 6 100 120 202 6G 2 20 5 42 6H 2 300132 214 6I 3 300 183

As is apparent from the results set forth in Table 6, compositions 6Band 6D exhibit etch rates significantly less than the control and Wpolishing rate only marginally less than the control. Compositions 6C(high concentration) and 6G exhibit both etch rates and W polishingrates that are significantly less than the control.

It will be understood that the recitation of ranges of values herein aremerely intended to serve as a shorthand method of referring individuallyto each separate value falling within the range, unless otherwiseindicated herein, and each separate value is incorporated into thespecification as if it were individually recited herein. All methodsdescribed herein can be performed in any suitable order unless otherwiseindicated herein or otherwise clearly contradicted by context. The useof any and all examples, or exemplary language (e.g., “such as”)provided herein, is intended merely to better illuminate the inventionand does not pose a limitation on the scope of the invention unlessotherwise claimed. No language in the specification should be construedas indicating any non-claimed element as essential to the practice ofthe invention.

Preferred embodiments of this invention are described herein, includingthe best mode known to the inventors for carrying out the invention.Variations of those preferred embodiments may become apparent to thoseof ordinary skill in the art upon reading the foregoing description. Theinventors expect skilled artisans to employ such variations asappropriate, and the inventors intend for the invention to be practicedotherwise than as specifically described herein. Accordingly, thisinvention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw. Moreover, any combination of the above-described elements in allpossible variations thereof is encompassed by the invention unlessotherwise indicated herein or otherwise clearly contradicted by context.

The invention claimed is:
 1. A chemical mechanical polishing composition comprising: a water based liquid carrier; a colloidal silica abrasive dispersed in the liquid carrier, the colloidal silica abrasive having a permanent positive charge of at least 6 mV; an amine containing polymer in solution in the liquid carrier; and an iron containing accelerator.
 2. The composition of claim 1, wherein the colloidal silica has a permanent positive charge of at least 15 mV.
 3. The composition of claim 1, wherein the colloidal silica is treated with an aminosilane compound selected from the group consisting of such as bis(2-hydroxyethyl)-3-aminopropyl trialkoxysilane, diethylaminomethyltrialkoxysilane, (N,N-diethyl-3-aminopropyl)trialkoxysilane), 3-(N-styrylmethyl-2-aminoethylaminopropyl trialkoxysilane, aminopropyl trialkoxysilane, (2-N-benzylaminoethyl)-3-aminopropyl trialkoxysilane), trialkoxysilyl propyl-N,N,N-trimethyl ammonium chloride, N-(trialkoxysilylethyl)benzyl-N,N,N-trimethyl ammonium chloride, (bis(methyldialkoxysilylpropyl)-N-methyl amine, bis(trialkoxysilylpropyl)urea, bis(3-(trialkoxysilyl)propyl)-ethylenediamine, bis(trialkoxysilylpropyl)amine, bis(trialkoxysilylpropyl)amine, and mixtures thereof.
 4. The composition of claim 1, wherein the iron containing accelerator comprises a soluble iron containing catalyst and the polishing composition further comprises a stabilizer bound to the soluble iron containing catalyst, the stabilizer being selected from the group consisting of phosphoric acid, phthalic acid, citric acid, adipic acid, oxalic acid, malonic acid, aspartic acid, succinic acid, glutaric acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, maleic acid, glutaconic acid, muconic acid, ethylenediaminetetraacetic acid, propylenediaminetetraacetic acid, and mixtures thereof.
 5. The composition of claim 1, further comprising a hydrogen peroxide oxidizer.
 6. The composition of claim 1, having a pH in a range from about 2.0 to about 3.5.
 7. The composition of claim 1, wherein the amine containing polymer is selected from the group consisting of triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polymers including the following amine containing functional groups methacryloylox-ethyl trimethyl ammonium methylsulfate, diallyl dimethyl ammonium chloride, and methacrylamido-propyl trimethyl ammonium chloride, and mixtures thereof.
 8. A method of chemical mechanical polishing a substrate including a tungsten layer, the method comprising: (a) contacting the substrate with a polishing composition comprising: (i) a water based liquid carrier; (ii) a colloidal silica abrasive dispersed in the liquid carrier, the colloidal silica abrasive having a permanent positive charge of at least 6 mV; (iii) an amine containing polymer in solution in the liquid carrier; and (iv) an iron containing accelerator; (b) moving the polishing composition relative to the substrate; and (c) abrading the substrate to remove a portion of the tungsten from the substrate and thereby polish the substrate.
 9. The method of claim 8, wherein the colloidal silica has a permanent positive charge of at least 15 mV.
 10. The method of claim 8, wherein the colloidal silica is treated with an aminosilane compound selected from the group consisting of such as bis(2-hydroxyethyl)-3-aminopropyl trialkoxysilane, diethylaminomethyltrialkoxysilane, (N,N-diethyl-3-aminopropyl)trialkoxysilane), 3-(N-styrylmethyl-2-aminoethylaminopropyl trialkoxysilane, aminopropyl trialkoxysilane, (2-N-benzylaminoethyl)-3-aminopropyl trialkoxysilane), trialkoxysilyl propyl-N,N,N-trimethyl ammonium chloride, N-(trialkoxysilylethyl)benzyl-N,N,N-trimethyl ammonium chloride, (bis(methyldialkoxysilylpropyl)-N-methyl amine, bis(trialkoxysilylpropyl)urea, bis(3-(trialkoxysilyl)propyl)-ethylenediamine, bis(trialkoxysilylpropyl)amine, bis(trialkoxysilylpropyl)amine, and mixtures thereof.
 11. The method of claim 8, wherein the iron containing accelerator comprises a soluble iron containing catalyst and the polishing composition further comprises a stabilizer bound to the soluble iron containing catalyst, the stabilizer being selected from the group consisting of phosphoric acid, phthalic acid, citric acid, adipic acid, oxalic acid, malonic acid, aspartic acid, succinic acid, glutaric acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, maleic acid, glutaconic acid, muconic acid, ethylenediaminetetraacetic acid, propylenediaminetetraacetic acid, and mixtures thereof.
 12. The method of claim 8, wherein the polishing composition further comprises a hydrogen peroxide oxidizer.
 13. The method of claim 8, wherein the amine containing polymer is selected from the group consisting of triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polymers including the following amine containing functional groups methacryloylox-ethyl trimethyl ammonium methylsulfate, diallyl dimethyl ammonium chloride, and methacrylamido-propyl trimethyl ammonium chloride, and mixtures thereof. 